The belt drive under discussion are those that rely upon friction to transfer power and not mechanical means such as teeth on the belt and pulley. The belt drive system of power transmission was one of the earliest methods of transmitting rotational energy from one location to another and is still widely used today.
Two factors which must be present for any drive to work properly are:
1. There must be sufficient surface contact area between belt and pulley so that the gripping force of the drive is greater than the resistance of the load. PA1 a. capable of engaging belt in either clockwise or counter-clockwise directions, PA1 b. capable of automatically disengaging (free-wheeling), PA1 c. lightweight, and PA1 d. simple and reliable. PA1 (a) To provide a belt tensioner that will engage the drive belt when either clockwise or counter-clockwise energy is applied. PA1 (b) To provide a state of neutral, effectively disengaging the driven pulley from the drive pulley, thus allowing the driven pulley to free-wheel. PA1 (c) To increase belt wrap for maximum surface contact, thus increasing load pulling capability. PA1 (d) To provide guides for the purpose of retaining the belt in the free-wheeling mode. PA1 (e) To provide a tensioner that will automatically compensate for belt wear. PA1 (f) To provide a tensioner that requires no RPM build-up, such as required with centrifugal clutches. PA1 (g) To provide a device that needs only the existing drive shaft for mounting. PA1 (h) To provide a tensioner that responds instantly to torque and direction. PA1 (i) To provide a device that is simple and light, free from heavy complicated gears and housings. PA1 (j) To provide a tensioner that will work equally as well with a fixed pulley or variable pitch sheave. PA1 (k) To provide a device for drive belt tensioning that does not require a lowering of the drive gear ratio.
2. There must be sufficient tension on the belt to maintain that surface contact. When this condition is met, the belt will tend to pull itself into the groove.
If we reflect on these elements it becomes apparent that to raise drive efficiency, increasing belt contact is preferable over increased belt tension. Multiple belts and wrapping the belt around the pulley are two methods that depend on this element.
Belt tension does play an important role in the operation of these devices, for without tension there would be little surface contact, excessive slippage between drive pulley and drive belt would occur. Therefore, only minor resistance would totally defeat the transfer of power. This factor can also be used as a plus when a neutral or free wheeling mode is desired.
According to the invention an ideal belt tensioner would possess the following characteristics: